[css-layout-api] Initial parts of contentSize callback.

Author: bfgeek

css-layout-api/Overview.bs

@@ -156,6 +156,8 @@ Layout Children {#layout-children}
 <pre class='idl'>
 [Exposed=LayoutWorklet]
 interface LayoutChild {
+    readonly attribute StylePropertyMapReadOnly styleMap;
+
     FragmentRequest layoutNextFragment(ConstraintSpace space, ChildBreakToken breakToken);
 };
 
@@ -165,7 +167,6 @@ interface InlineLayoutChild : LayoutChild {
 
 [Exposed=LayoutWorklet]
 interface BoxLayoutChild : LayoutChild {
-    readonly attribute StylePropertyMapReadOnly styleMap;
 };
 </pre>
 
@@ -206,7 +207,7 @@ Note: In a future level of the specification there may be a way to query the com
       of ranges inside a {{InlineLayoutChild}}.
 
 A {{BoxLayoutChild}} represents a single <a>box</a>. It does have an associated computed style which
-can be accessed by {{BoxLayoutChild/styleMap}}. The {{BoxLayoutChild/styleMap}} will only contain
+can be accessed by {{LayoutChild/styleMap}}. The {{LayoutChild/styleMap}} will only contain
 properties which are listed in the child input properties array.
 
 A {{BoxLayoutChild}} could be generated by:
@@ -777,6 +778,9 @@ A <dfn>layout definition</dfn> is a <a>struct</a> which describes the informatio
  - <dfn for="layout definition">layout generator function</dfn> which is the layout <a>generator
      function</a> callback.
 
+ - <dfn for="layout definition">content size generator function</dfn> which is the content size
+     <a>generator function</a> callback.
+
  - <dfn for="layout definition">constructor valid flag</dfn>.
 
  - <dfn for="layout definition">input properties</dfn> which is a <a>list</a> of
@@ -905,12 +909,22 @@ is called, the user agent <em>must</em> run the following steps:
     18. If |layout|'s <code>\[[FunctionKind]]</code> internal slot is not <code>"generator"</code>,
         <a>throw</a> a <a>TypeError</a> and abort all these steps.
 
-    19. Let |definition| be a new <a>layout definition</a> with:
+    19. Let |contentSize| be the result of <a>Get</a>(|prototype|, <code>"contentSize"</code>).
+
+    20. If the result of <a>IsCallable</a>(|contentSize|) is false, <a>throw</a> a <a>TypeError</a>
+        and abort all these steps.
+
+    21. If |contentSize|'s <code>\[[FunctionKind]]</code> internal slot is not
+        <code>"generator"</code>, <a>throw</a> a <a>TypeError</a> and abort all these steps.
+
+    22. Let |definition| be a new <a>layout definition</a> with:
 
         - <a>class constructor</a> being |layoutCtor|.
 
         - <a>layout generator function</a> being |layout|.
 
+        - <a>content size generator function</a> being |contentSize|.
+
         - <a>constructor valid flag</a> being <b>true</b>.
 
         - <a for="layout definition">input properties</a> being |inputProperties|.
@@ -919,9 +933,9 @@ is called, the user agent <em>must</em> run the following steps:
 
         - <a for="layout definition">child display</a> being |childDisplay|.
 
-    20. <a for=map>Set</a> |layoutDefinitionMap|[|name|] to |definition|.
+    23. <a for=map>Set</a> |layoutDefinitionMap|[|name|] to |definition|.
 
-    21. <a>Queue a task</a> to run the following steps:
+    24. <a>Queue a task</a> to run the following steps:
 
         1. Let |documentLayoutDefinitionMap| be the associated <a>document's</a> <a>document layout
             definitions</a> <a>map</a>.
@@ -964,6 +978,10 @@ is called, the user agent <em>must</em> run the following steps:
             static get childrenInputProperties() { return ['--bar']; }
             static get childDisplay() { return 'normal'; }
 
+            *contentSize(children, styleMap) {
+                // min/max content size code goes here.
+            }
+
             *layout(constraintSpace, children, styleMap, breakToken) {
                 // Layout code goes here.
             }
@@ -983,11 +1001,17 @@ interface FragmentRequest {
   // [[constraintSpace]] - The constraint space to perform layout in.
   // [[breakToken]] - The break token to resume the layout with.
 };
+
+[Exposed=LayoutWorklet]
+interface ContentSizeRequest {
+  // Has internal slots:
+  // [[layoutChild]] - The layout child to calculate the content size for.
+};
 </pre>
 
-The layout method on the author supplied layout class is a generator function instead of a regular
-javascript function. This is for user-agents to be able to support asynchronous and parallel layout
-engines.
+The layout method and content size method on the author supplied layout class is a generator
+function instead of a regular javascript function. This is for user-agents to be able to support
+asynchronous and parallel layout engines.
 
 When an author invokes the {{LayoutChild/layoutNextFragment()}} method on a {{LayoutChild}} the
 user-agent doesn't synchronously generate a {{Fragment}} to return to the author's code. Instead it
@@ -1018,7 +1042,7 @@ class LayoutEngine {
   // This function takes a FragmentRequest and calls the appropriate layout
   // algorithm to generate the a Fragment.
   layoutFragment(fragmentRequest) {
-    const box = fragmentRequest.box;
+    const box = fragmentRequest.layoutChild;
     const algorithm = selectLayoutAlgorithmForBox(box);
     const fragmentRequestGenerator = algorithm.layout(
         fragmentRequest.constraintSpace,
@@ -1060,6 +1084,11 @@ dictionary FragmentResultOptions {
     BreakTokenOptions breakToken = null;
     double alignmentBaseline = null;
 };
+
+dictionary ContentSizeResultOptions {
+    double maxContentSize;
+    double minContentSize;
+};
 </pre>
 
 Issue: Specify how we do min/max content contributions.